I don't know for sure how it works, but my DS, who is a C4C wanted to take Spanish, and he was placed in Arabic. Also, my older son, a grad of USMA, also wanted Spanish and was given Arabic. From these experiences, I'm not seeing any indication that you always get your first choice in foreign language.

If I remember correctly, you will take one or more language placement tests during Basic (I think). You will be placed in a language based on your aptitude (the test(s) do not test a specific language -- they test aptitude to learn a foreign language). My daughter -- who had had 4 years of High School Spanish -- was placed in Russian. Not because that's what she wanted to take but because it was one of the languages the military needs. Other similar languages are Arabic and Chinese. (there's a word/phrase for this kind of priority language -- I just don't remember it). One of my daughter's friends was allowed to continue in her high school language -- Portuguese -- but that was an oddity. Most of my daughter's friends were placed in Russian, Chinese, Arabic, etc. I think this is covered in one of the books the Academy sent us before IDay about majors, class offerings, etc. My daughter was required to complete 2 years of Russian and was then done with a foreign language.

I think the term you're looking for is "strategic language" and I understand that many C4Cs were placed in Chinese and Arabic despite (or maybe because of) having several years in high school in more traditional high school languages such as Spanish and French. I do know of a couple of C4Cs who were placed in high level French and Spanish classes, but my anecdotal information indicates that C4Cs being placed in beginner classes are usually placed in Chinese, Arabic and Russian.